Her is a tip.
Unless you know for sure that your factory ICM is toast don't replace it with the garbage they're selling us now.
The day after I bought my truck I got under the hood and started making a list of parts that needed replacing. Most of it was the basic tune up parts. Plugs, wires, cap, rotor, air filter, fuel filter and PCV valve(which turned out to be junk and I had to clean the original). While I was replacing the cap and rotor I discovered the pickup coil was in bad shape and the top bushing in the dist. was worn so I bought a new dist. The new dist. came with the ICM already installed so I dropped it in,set the base timing and the truck ran fine. Here in the past week or so I've been upgrading the ECM to the 12277427 PCM that was used in 93-95 trucks and have started datalogging and tuning. While I was playing back a log session I noticed little oscillations in the tach line on the monitor and figured that was just the way it was. While trying to figure out what the engine liked for ignition timing at idle I had my timing light on it and noticed I was getting extra flashes from the light but still the engine ran good,,,,,,,,or so I thought. I got to thinking about the wiggles in the tach data and the extra flashes so I put my original factory ICM back in. No more extra flashes and the tach data line is smooth. Because I'm still tuning I can't say that it runs better but I can say the ignition system is working better.
Unless you know for sure that your factory ICM is toast don't replace it with the garbage they're selling us now.
The day after I bought my truck I got under the hood and started making a list of parts that needed replacing. Most of it was the basic tune up parts. Plugs, wires, cap, rotor, air filter, fuel filter and PCV valve(which turned out to be junk and I had to clean the original). While I was replacing the cap and rotor I discovered the pickup coil was in bad shape and the top bushing in the dist. was worn so I bought a new dist. The new dist. came with the ICM already installed so I dropped it in,set the base timing and the truck ran fine. Here in the past week or so I've been upgrading the ECM to the 12277427 PCM that was used in 93-95 trucks and have started datalogging and tuning. While I was playing back a log session I noticed little oscillations in the tach line on the monitor and figured that was just the way it was. While trying to figure out what the engine liked for ignition timing at idle I had my timing light on it and noticed I was getting extra flashes from the light but still the engine ran good,,,,,,,,or so I thought. I got to thinking about the wiggles in the tach data and the extra flashes so I put my original factory ICM back in. No more extra flashes and the tach data line is smooth. Because I'm still tuning I can't say that it runs better but I can say the ignition system is working better.
